铁电薄膜铁电性能的测量

本文介绍了铁电薄膜材料铁电性能的测量原理和方法.分析了以传统测量电路Sawyer-Tower电路为基础的电滞回线测量方法和基于虚地模式的电滞回线测量方法,并提出了一种基于计算机的铁电性能综合测试仪的实现方案,对其中的主要部分微电流放大器的设计作了介绍.该测试仪不仅能画出铁电薄膜的电滞回线,还可以得到铁电薄膜材料的饱和极化Ps、剩余极化Pr、矫顽场Ec、漏电流Ik等参数,以及对铁电薄膜材料的铁电疲劳性能、铁电保持性能的测试.     

溶胶-凝胶法制备Mg0.2Zn0.8O阻变薄膜的研究

采用溶胶-凝胶工艺在氧化铟锡(ITO)玻璃衬底上制备Mg0.2Zn0.8O阻变薄膜,研究了退火温度和薄膜层数对Mg0.2Zn0.8O薄膜生长行为、漏电流性能的影响。研究发现,Mg0.2Zn0.8O薄膜是多晶态结晶结构,薄膜的(100)、(002)和(101)晶面所对应衍射峰的强度随镀制薄膜层数的增多和退火温度的升高明显增强。结果表明,随退火温度的升高,高阻态(HRS)和低阻态(LRS)的漏电流减小;然而,HRS时薄膜的漏电流却随Mg0.2Zn0.8O薄膜层数的增多而变大。退火温度和薄膜厚度改变Mg0.2Zn0.8O阻变薄膜中氧空穴和缺陷的数量,进而影响Mg0.2Zn0.8O薄膜的漏电流。     

单相无变压器光伏并网系统漏电流的研究

漏电流是研究非隔离型光伏并网系统的一个重要问题.漏电流谐振电路等效模型的建立对研究抑制漏电流至关重要.本文首先推导单相全桥并网逆变器漏电流谐振回路等效电路模型;然后详细分析了不同开关调制方式和滤波电感不对称分布对漏电流的影响,并指出电网电压对漏电流的影响不可忽略;最后介绍了一种新型无变压器拓扑结构,这种结构具有单极性调制和双极性调制优点,能够抑制共模漏电流的产生,同时提高系统的效率和并网电流质量.通过仿真和实验验证了分析结果的正确性.     

无变压器非隔离型光伏并网逆变器漏电流抑制技术

漏电流抑制是无变压器型光伏并网系统需要解决的关键问题之一。VDE-0126-1-1标准规定,漏电流高于300 mA时光伏并网系统必须在0.3 s内从电网中切除。为了解释漏电流的根源,建立系统共模电压数学模型,在此基础上分析漏电流产生的原因,探讨不同调制策略对漏电流的影响,然后介绍几种典型的、能够有效抑制漏电流的电路拓扑结构,并分析各种拓扑的工作原理和特点。最后对漏电流抑制技术方面的发展趋势做了展望。     

基于谐波提取的非隔离型并网光伏逆变器漏电流检测研究

与隔离型逆变器相比,非隔离型并网光伏逆变器体积小、成本低、效率高,但往往容易产生共模漏电流,相应安全隐患增大,相关标准对漏电流抑制及保护提出了严格要求。该文对上述情况的漏电流问题进行研究,详细分析单相Boost+HERIC逆变拓扑漏电流产生机理及漏电流谐波特征,然后分析漏电流检测硬件系统的局限性。在此基础上提出一种基于谐波提取的漏电流检测方法,有效解决了含有高频谐波漏电流检测不准确问题,实现了持续漏电流、突变漏电流的准确检测及保护。通过仿真及实验结果验证机理分析的正确性及侦测方法的有效性。该方法对含有高频漏电流的其他单相逆变拓扑及三相逆变拓扑均可使用。     

PWM电机系统漏电流分析

随着PWM变频器在电机控制中的广泛应用,在电机控制性能显著提高的同时,系统共模电流(正常漏电流)的问题愈发严重。同时,当电机系统发生漏电故障时,现有漏电保护装置不能区分故障漏电流和正常漏电流,导致系统存在安全隐患。针对此问题,首先对PWM电机系统正常漏电流计算模型和流通路径进行研究,然后对系统的漏电故障点及相应故障漏电流进行了分析,最后通过试验测试对PWM电机系统正常漏电流和正常与故障混合漏电流的时频特性进行深入分析和研究,为正常漏电流的有效抑制和故障漏电流的准确检测提供理论指导。     

单相非隔离型光伏并网系统漏电流分析

抑制漏电流已成为非隔离型光伏并网系统研究的重要技术问题。考虑到漏电流在光伏并网系统中的重要性,文章首先建立漏电流谐振电路等效模型,指出传统H4拓扑结构的不足,并分析漏电流产生原理。然后介绍了一种能够有效抑制漏电流的新型拓扑结构,分析其工作原理和并网控制方法,最后在一台2k W的实验样机上进行实验验证,结果表明该新型拓扑结构的光伏并网逆变器能较好的抑制漏电流。     

Bi4Ti3O12铁电薄膜的制备及研究进展

铁电薄膜具有良好的铁电、介电性能,在非挥发存储器件方面有很好的应用前景.本文介绍了钛酸铋(Bi4Ti3O12)铁电薄膜的研究现状,对目前Bi4Ti3O12铁电薄膜最常用的几种主要制备方法及其掺杂改性进行了评述,指出了Bi4Ti3O12铁电薄膜研究中亟待解决的几个问题.     

基于方波脉冲电压绝缘寿命实验的漏电流检测

在脉冲电应力绝缘加速老化实验中,为消除试样电容过渡过程电流对绝缘材料和结构绝缘失效判定的影响,提高实验结果的准确性和可靠性,设计一种漏电流检测电路。在双极性高频脉冲电压下电容过渡过程电流主要集中在脉冲边沿5μs以内,12μs后过渡过程基本结束,此后试样回路电流主要是绝缘漏电流;利用此特性,通过控制电路控制电子开关,在每个脉冲边沿切除电容过渡电流而代以前一时刻的漏电流保持值,而12μs后再切换回电流检测信号。理论分析和实验结果表明,该漏电流检测方法可以有效的消除试样等效电容过渡过程电流对漏电流检测的影响,其相对偏差率小于3.03%,可以较好的满足脉冲电应力绝缘寿命加速老化实验的要求,且提高实验结果的可靠性。     

基于多载波实现光伏并网逆变器漏电流抑制研究

无隔离光伏并网逆变器具有成本低和体积小等优点而备受关注。但光伏电池板和大地之间的寄生电容和电感会产生漏电流问题,漏电流会影响逆变器寿命,严重时甚至危害人身安全。本文通过建模分析光伏并网逆变器漏电流和共模电压有关,而共模电压和逆变器的矢量成一定关系,从而可以发现漏电流主要是零矢量产生的。故本文提出一种多载波调制摒弃零矢量的方法,从而实现光伏并网逆变器漏电流抑制,该方法在不增加硬件和成本的情况下实现漏电流的抑制。在光伏并网逆变系统中,设计合适的电流控制器对系统稳定性和电能质量至关重要。本文采用准PR(proportional resonant,PR)控制器实现快速精准控制,省去了复杂的坐标变化。通过仿真验证了所提算法的正确性。     

Effect of vanadium doping on ferroelectric and electrical properties of Bi3.25La0.75Ti3O12 thin film

Bi_3.25La_0.75Ti₃O₁₂ (BLT) and V-doped BLT (BLTV) thin films were prepared on Pt/Ti/SiO₂/Si substrates by a pulsed laser deposition method. The effects of V doping on ferroelectric and electrical properties were investigated by polarization-electric field hysteresis loops and leakage current-voltage measurements. BLTV single phases were confirmed by X-ray diffraction. Remnant polarization was increased and the leakage current density was decreased by V doping. The leakage current density of BLT thin films suddenly increased at 100 kV/cm while that of BLTV thin films increased at the higher electric field of 160 kV/cm. The power law relationship J α Eⁿ of current density vs. applied electric field is estimated to be J αE^2.0 for BLT and J αE^1.0 for BLTV thin films. The leakage current of the BLT/Pt junction can be explained by space-charge-limited current. However, that of the BLTV/Pt junction was characterized by the Schottky emission behavior.     

Micro-structure and ferroelectric properties of BiFeO3 thin films formed on Pt-coated r-plane sapphire substrates

Magnetoelectric BiFeO₃ (BFO) materials exhibit ferroelectric and ferromagnetic properties simultaneously, therefore they have a potential to be applied in magnetic as well as ferroelectric devices. BFO thin films were formed by depositing sol-gel solutions on Pt-coated r-plane sapphire dielectric substrates. We did not observe any secondary phase such as Bi₂Fe₄O₉ on the r-plane sapphire substrates, which is generally observed on Si substrates. We observed small ferroelectric grains of about 0.1 μm on Pt/sapphire structures. The leakage current density in BFO films was found to be decreased dramatically after optimizing process conditions of stoichiometric BFO chemical solution. The leakage current densities were in the range of 10^{− 7} A/cm² at room temperature and 10^{− 9} A/cm² at 80 K under 0.4 MV/cm applied electric field. The main reason for low leakage current is considered to be reduction of oxygen vacancies due to the presence of exclusive Fe^{3 +} valance state in the films. An applied electric field higher than 0.5 MV/cm was required to pole the BFO films, which made it difficult to obtain the saturated polarization at room temperature. We could measure the saturated remanent polarization in the BFO films at 80 K and the obtained remanent polarization was 100 μC/cm².     

SbSI Films for Ferroelectric Memory Applications

Films of ferroelectric antimony sulphoiodide (SbSI) were grown on platinized silicon substrates by pulsed laser deposition (PLD). The films were grown at room temperature and later annealed at 200-250 C in air for crystallinity. The Curie temperature (T C ) of these films was 17-21 C, whereas the peak dielectric constant was up to 5000. These films showed nonzero remnant polarization above T C up to a temperature of 40 C and a low leakage current density of around 10 m 6 A/cm 2 at 2V. SbSI films were integrated with colossal magnetoresistive La 0.67 Ca 0.33 MnO 3 (LCMO) thin film, which acts as a p-type semiconductor. The LCMO-SbSI heterostructures, with SbSI as a ferroelectric gate, showed a channel modulation of about 10%.     

Preparation of Si-Added SrBi2Ta2O9 Ferroelectric Thin Films by RF Magnetron Sputtering

Si-added SrBi₂Ta₂O₉ (SBT) ferroelectric films were prepared by RF magnetron sputtering on a Pt/Ti/SiO₂/Si (100) structure. The films were deposited at temperatures below 100°C for surpressing Bi evaporation, and crystallized at 800°C in air. A typical composition was Sr_0.79Bi_2.37Ta_2.00Si_0.2O_x. The remanent polarization value (2Pr) of the Si-added SBT film was 16 μC/cm². The Si atom addition was found to be effective in improvement of the fatigue and leakage current of SBT ferroelectric films. The leakage current density was further improved by annealing in the high-pressure oxygen ambient at 7 atms.     

Structure and Properties of Preferential (110) Orientation BiFeO3 Thin Films by Sol-Gel Method

Abstract

Multiferroic materials, coexisting of ferroelectric, ferromagnetic and ferroelastic properties, possess potential applications in functional devices. BiFeO₃ (BFO) is a unique room temperature multiferroic material with high ferroelectric Curie temperature and Neel temperature. The BFO thin films were prepared on Si (111) substrate by sol-gel method in this paper. XRD analyses show that the thin films exhibit pure phase and preferred (100) orientation when annealing temperature is 500?°C. Field emission scanning electron microscopy shows that the crystallization degree of the films is getting better with the increase of annealing temperature. The thickness of the sample is about 400?nm. The hysteresis loop of BFO films annealing at 500?°C show 1.93?µC/cm² remnant polarizations. However, the hysteresis loop is not perfect, which may be caused by a large leakage current. The magnetic hysteresis loop of BFO films is tested as well, indicating that the BFO film is antiferromagnetic and the residual magnetization (Mr) and coercive field (Hc) of the BFO films were 0.054?emu/g and 1026.4?Oe, respectively.     

Electrical and Ferroelectric Properties of the Bi3.9La0.1Ti2.9V0.1O12 (BLTV) Thin Films

On the SiO₂/Si(100) substrates, Bi_3.9La_0.1Ti_2.9V_0.1O₁₂ (BLTV) ferroelectric thin films were deposited to form a metal-ferroelectric-metal (MFM) structures and improved by the low temperature supercritical carbon dioxide fluid (SCCO₂) post-treatment process. The dielectric and ferroelectric characteristics of the as-deposited BLTV thin films were measured and investigated by the XPS, C-V, and J-E measurement. From the measured results, after the SCCO₂ post-treatment, the capacitance, leakage current density, coercive field, and remnant polarization of the BLTV thin films were all improved obviously. Finally, the mechanism concerning the dependence of electrical properties of the ferroelectric thin films was also investigated.     

La doped PZT 60/40 films by MOD technology

Abstract

Ferroelectric La doped PZT 60/40 thin films with uniform composition have been synthesized using metallo-organic precursor solutions. These metallo-organic precursors have been stored for more than four years and are very stable in ambient conditions, compared to the sol-gel solutions. The structural properties of these films have been studied using X-ray diffraction and atomic force microscopy. The excellent ferroelectric properties of the films, such as less than 10% polarization loss after 10¹¹ cycles, low leakage current of 3·06×10^?12 A at 2 V, and small separation of polarization peaks in a voltage loop by the small-signal measurement, are attributed to the high quality of the metalloorganic solutions used in this study, which have been carefully home-synthesized. The oxygen vacancy in the films was reduced by optimizing the annealing conditions, and to minimize the blocking oxygen vacancy at the interface by Pt electrodes a suitable amount of La ions was doped. We suggest that greater attention should be paid to the elimination/minimization of the oxygen vacancy in the ferroelectric PZT films instead of using oxide electrodes, which allow a relatively larger leakage current flowing through the films and the electrodes.     

Electrochemical models of failure in oxide perovskites

Abstract

Electrochemical models of failure in oxide perovskite materials are reviewed. It is noted that oxygen vacancies are a common source of electrical degradation, fatigue, and ageing. Taking the behavior of oxygen vacancies into account, a semi-quantitative model for time dependent dielectric breakdown (TDDB) is proposed and a quantitative fatigue mechanism is discussed for ferroelectric thin films. Based on the fatigue theory, a recent improvement in fatigue of ferroelectric thin films is presented. Correlation between leakage current and fatigue is also presented.     

Growth and Ferroelectric Characterization of Cerium-Modified Bismuth Titanate Thin Film Deposited on GaN Substrate by Pulsed Laser Deposition

Cerium-modified Bi₄Ti₃O₁₂ thin films were deposited on GaN substrates by the pulsed laser deposition method. The substrate temperature was varied from 600°C to 750°C in 50°C steps. The surface topographies and orientations of the Bi_0.4Ce_0.6Ti₃O₁₂ (BCeT) films were gradually changed in proportion to the substrate temperature. The diffusion reaction between BCeT and the GaN layer and the depth profiles of the films were investigated by Auger electron spectroscopy (AES). The ferroelectric properties and leakage current characteristics of the metal-ferroelectric-GaN stacked thin films were measured and discussed.     

DC conduction behavior of Bi3.15Nd0.85Ti3O12 thin films grown by RF-magnetron sputtering

The Bi_3.15Nd_0.85Ti₃O₁₂ (BNT) thin films were deposited on Pt(111)/Ti/SiO₂/Si substrates by using RF-magnetron sputtering method and studied the ferroelectric and leakage current charateristics. The polarization – electric field (P-E) hysteresis loops of BNT film was well saturated with the remnant polarization (2P _r ) of 29.8 μC/cm² and a coercive field (2E _c ) of 121 kV/cm. The leakage current density – electric field (J-E) characteristics of the Pt/BNT/Pt capacitor reveals the presence of two conduction region, having Ohmic behavior at low electric field (below 50 kV/cm) and Schottky-emission or Poole-Frenkel emission at high electric field (above 60 kV/cm). The barrier height and trapped level of BNT films are estimated to be 1.11 eV and 0.90 eV, respectively.